1. Field of the Invention
The present invention relates to a method of calculating a positional relationship, with respect to a running path on a road, of a motor vehicle which is automatically steered to run along the running path while detecting magnetic sources or magnetic nails that are arranged on the road at spaced intervals along the running path.
2. Description of the Related Art
There has been proposed in recent years an automatic motor vehicle drive system wherein magnetic nails are embedded in a road at spaced intervals along a running path on the road and detected by a sensor on a motor vehicle to automatically steer the motor vehicle to run along the running path based on magnetic forces produced by the magnetic nails and detected by the sensor.
In the conventional automatic motor vehicle drive system, the sensor for detecting the magnetic nails is mounted in one location on the bottom of the motor vehicle at a front or rear end thereof.
For automatically steering the motor vehicle to run along the running path, the conventional automatic motor vehicle drive system needs to accurately recognize a positional relationship between the motor vehicle and the running path, including a lateral deviation of the motor vehicle from the running path, i.e., a positional displacement in the transverse direction of the motor vehicle with respect to the running path, and an azimuth deviation of the motor vehicle with respect to the running path, i.e., an angle formed between the traveled direction in which the motor vehicle travels and the running path.
Because only one magnetic nail sensor is mounted on the motor vehicle, it is difficult to accurately determine the lateral deviation of the motor vehicle from the running path and the azimuth deviation while the motor vehicle is running. Consequently, it has been customary to rely upon a sensing system other than the magnetic sensor for recognizing the lateral deviation and the azimuth deviation.
For example, a process has been proposed to produce an image of a road ahead of a motor vehicle with a CCD camera mounted on the motor vehicle, and measure the position of the motor vehicle in the transverse direction of the road and the azimuth angle based on the position and direction of white lines coated on the road which are contained in the produced image. One problem with this proposed process is that the detecting capability of the CCD camera may be greatly impaired if the environment of the road is made poor by weather conditions such as rain, snow, etc. If the CCD camera fails to detect the position and direction of white lines on the road, then the lateral deviation and azimuth angle of the motor vehicle cannot accurately be measured.
According to another proposal, a yaw rate sensor is mounted on a motor vehicle to calculate a traveled route along which the motor vehicle has been running. The positional relationship of the motor vehicle with respect to the running path, including a positional displacement and an azimuth deviation of the motor vehicle, is recognized on the basis of the calculated traveled route. However, as the motor vehicle travels an increased distance, detection errors of the yaw rate sensor are accumulated, resulting in difficulty accurately recognizing the positional relationship of the motor vehicle with respect to the running path, including a positional displacement and an azimuth deviation of the motor vehicle.